58In that regard, it must be recalled that the function of a limitation period is to ensure legal certainty and that that fundamental requirement prevents the administration from indefinitely delaying the exercise of its powers (see, to that effect, judgments of 10 June 2004, François v Commission, T‑307/01, EU:T:2004:180, paragraphs 45 and 46, and of 8 March 2012, Kerstens v Commission, F‑12/10, EU:F:2012:29, paragraphs 122 and 123). Consequently, in the presence of provisions laying down limitation periods for the initiation of disciplinary proceedings, there is no room for any consideration relating to a reasonable period (see, to that effect and by analogy, judgments of 13 November 2014, Nencini v Parliament, C‑447/13 P, EU:C:2014:2372, paragraphs 52 to 54, and of 18 June 2008, Hoechst v Commission, T‑410/03, EU:T:2008:211, paragraph 224). While it has been accepted that the time limits for disciplinary proceedings were not mandatory, this has been held to be the case only for those relating to the conduct of the proceedings (judgment of 17 March 2015, AX v ECB, F‑73/13, EU:F:2015:9, paragraph 174; see also, as regards the time limits referred to in Section 5 of Annex IX to the Staff Regulations of Officials of the European Union, judgment of 8 March 2012, Kerstens v Commission, F‑12/10, EU:F:2012:29, paragraph 124), and not for those concerning their initiation.